Synthesis of the Bis(iron) Carbene Complex [Cp*(dppe)FeC(OMe)CHCHC(OMe)Fe(dppe)Cp*][PF₆]₂: A Binuclear Organometallic Compound with a Low-Spin ↔ High-Spin Interconversion

Abstract

The new diiron μ-bis(carbene) complex [Cp*(dppe)FeC(OCH3)-CHCHC−(OCH3)Fe(dppe)Cp*][PF6]2 (4) [Cp* = pentamethylcyclopentadienyl, dppe = ethylenebis(diphenylphosphine)] was obtained by double deprotonation of [Cp*(dppe)FeC(OCH3)CH2CH2C(OCH3)Fe(dppe)Cp*]·2[PF6] (2) with KOBut followed by a two-electron oxidation with 2 equiv of ferrocenium (80%). On the basis of the multinuclear NMR spectroscopy the complex 4 appeared as diamagnetic in solution. Temperature-dependent magnetic susceptibility measurements with a microcrystalline sample of 4 showed antiferromagnetic behavior. Isotropic spin-only models of the data derived magnetic exchange coupling constants of J = − 27.4 cm-1. Variable-temperature Mössbauer spectroscopy allowed the observation of both the singlet and triplet spin isomers and their interconversion. The time scale for the spin flipping is larger than 10-6 s, suggesting the existence of a thermal barrier between the two spin states.